Drilled holes in the ground are used for wells and for many different purposes, including the taking of samples from the ground--when exploring for minerals, for example, or when testing for the presence of contaminants in groundwater.
Such drilled holes are often provided with a steel liner or casing extending through the overburden. Sometimes, the steel liner does not extend to the full depth of the hole, and it becomes important for the engineer to determine to what depth the casing extends.
Previous attempts have been made to provide a probe which can be inserted into the ground-hole, and which will locate the bottom of the casing, and will indicate its depth. The present invention is aimed at providing a probe which is superior in performance and reliability to previous designs, which is quick and easy to deploy and use, yet which is simple and economical to manufacture.